The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 100 60 822.1, filed on Dec. 7, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The invention relates to a pressurized screen to remove contaminants from a contaminant-containing fibrous paper suspension with a vertical housing that contains at least two mainly axially symmetrical screen elements that are arranged so that the fibrous suspension fed through at least one intake into the housing can flow through them in succession. The upstream first screen element can be rotated and is mounted axially outside and above the chamber in which the second screen element is located. A part of the fibrous paper suspension that has passed through the second screen element is channeled out of the housing through at least one accepts outlet. The housing further includes at least one coarse reject outlet for the overflow of the first screen element and at least one fine reject outlet for the overflow of the second screen element.
The invention also relates to a pressurized screen to remove contaminants from a contaminant-containing fibrous paper suspension with a horizontal housing that contains at least two mainly axially symmetrical screen elements that are arranged so that the fibrous suspension channeled into the housing through at least one intake can flow through them in succession. The upstream first screen element can be rotated, and the part of the fibrous paper suspension that has passed the second screen element is channeled out of the housing through at least one accepts outlet. The housing features at least one coarse reject outlet for the overflow of the first screen element and at least one fine reject outlet for the overflow of the second screen element.
2. Discussion of Background Information
Pressurized screens are used in the processing of fibrous paper suspensions, in order to treat the fibrous suspension in a wet screening. To this end such a pressurized screen contains at least one screen element that is provided with a number of openings. The fibers contained in the suspension should pass through the openings, while the unwanted solid particles are rejected there and conveyed out of the screen again. As a rule, round holes or slits are used as screen openings. In most cases, pressurized screens of the kind considered here are equipped with screen scrapers that feature scraping areas swept across the screen. This is how the clogging of the screen openings is usually prevented in the per se known way.
As both the state of disintegration of the paper fiber material and the volume and structure of the contaminant content change constantly in the course of the pulp processing, it is necessary in many cases to operate pressurized screens in several stages with different openings. In this way it is possible to achieve overall a good straining of most of the contaminants collected. Such contaminants, which differ significantly from the other contaminants due to their sinking action, can thereby also be strained by means of hydro-cyclones. This technique is also known, so that a sequence of hydro-cyclones and pressurized screens is used for pulp screening in general.
A vertical separator for a fibrous suspension that features two screen elements in a single machine is known from DE 197 02 044 C1. With this separator, the pulp stream to be sorted first arrives at the area of a flat coarse screen that is kept clear on the intake side with a scraper. The flow through this flat coarse screen is then conducted into the interior of an axially symmetrical screen basket, through the openings of which the accepts pass, so that the suspended paper fibers can pass through this screen basket into the accepts outlet. This kind of screen should be used in particular whenever the supplied fibrous suspension is mixed with a larger amount of coarse contaminants. This is known to occur very often in waste paper processing, especially with the pulp that comes directly from the pulper or after passing through a cleaning device that removes only the coarsest impurities. However, in certain cases this known screen has the disadvantage that a high degree of wear occurs, particularly in the area of the flat primary screen, and the coarse impurities can lead to breakdowns.
WO 00/5 8549 A1 shows a screen with a vertical housing in which there are two screen elements through which the fibrous paper suspension to be cleaned flows successively. In this the two screen elements are at least partially axially fitted into one another, which facilitates a compact construction. Other versions with two screens flowed through successively are known from EP 0 955 406 A2 and DE 2140 904. The first screen is cylindrical and is set in rotation. However, these devices are unfavorable in many applications. This applies in particular to the processing of coarse pulps. A cylindrical screen has the disadvantage in particular that the oblong impurities with a tendency to spin or wind can easily stick to such a screen and then become firmly fastened as a result of the rotation. They can then only be removed manually after shutting down.
A flat, disk-shaped screen, such as is known from WO 00/52260, for instance, has a simple structure and takes up little space. However, it has only a small screen surface, which is disadvantageous.
The present invention provides a pressurized screen that is unsusceptible to clogging impurities and at the same time offers good screening quality. It may be particularly useable for disintegrated waste paper that still contains a large proportion of the originally contained, hardly crushed contaminants.
According to the instant invention, the first screen element has a conical form with an opening angle (xcex1) that is between about 10 and 170xc2x0. Moreover, in the horizontal orientation, the first screen element is positioned axially outside of and to the side of the chamber in which the second screen element is located.
A pressurized screen of the type of construction according to the invention is particularly suitable for use at the start of paper stock preparation, that is, wherever a relatively large proportion of coarser contaminants is still carried along in the suspension. If waste paper is brought into the pulper or cleaning drum in suspension, for instance, it often has a contaminant content of more than 2% of the solids. Part of this contaminant is relatively coarse and is therefore also rejected to a great extent at a 4 mm perforation.
After entering the pressurized screen according to the invention, the suspension encounters the intake side of the first screen element. Its rotation creates a centrifugal force with which the contaminants are spun from the surface of this screen element, provided they have a higher specific gravity than the suspension surrounding them. Thus not only the tractive forces created due to the pressure difference, but also centrifugal forces act on the solid particles located near the screen intake. The more the longitudinal direction of the screen opening is oriented radially (instead of axially), the stronger the free centrifugal effect and the lower the danger of the particles being caught in the openings. Heavy particles that are rejected at the screen element according to the specification, leave its intake area relatively quickly and are then removed from the housing through the coarse reject outlet. They may possibly also carry with them light contaminants rejected because of their size, particularly plastic foils. The screen is not only less at risk of wear, but it is also not so easily clogged by wire pieces, splinters of glass and small stones.
The centrifugal effect naturally depends on the speeds and the radius at the place in question. The particular advantage of the invention lies in the fact that the first screen element is constructed conically at least in part. A conical form combines the advantages of a large screen surface with sufficient centrifugal effect from the screen area.
Through the combination according to the invention of the two screen elements that work differently in one housing, a compact machine is created that works reliably even with heavily contaminated liquids. Another advantage is the possibility of being able to provide the first screen element and the scrapers for the second screen element with a common drive.
The pressurized screen according to the invention is easily equipped with an effective light contaminant discharge. Thus Styrofoam and foil pieces can already be concentrated and removed with the aid of centrifugal forces before they have passed the first screen element. The same applies to air. This collection and discharge of light particles is helped by a flat or conical first screen element.
The present invention is directed to a pressurized screen to remove contaminants from a contaminant-containing fibrous paper suspension. The pressurized screen includes a housing, a first screen element, which is essentially axially symmetric and is rotatably mounted within the housing, and a second screen element, which is essentially axially symmetric. The first and the second screen elements are successively arranged in a suspension flow direction. At least one intake, coupled to the housing, is structured and arranged to supply the suspension to the housing, and at least one accepts outlet, coupled to the housing, is structured and arranged to convey a part of the suspension that passes through the second screen element out of the housing. At least one coarse reject outlet is located within the housing to remove a part of the suspension not passing through the first screen element, and at least one fine reject outlet is located within the housing to remove a part of the suspension not passing through the second screen element. The first screen element includes a conical shape with an opening angle (xcex1) between about 10xc2x0 and 170xc2x0.
In accordance with a feature of the instant invention, the housing can be a vertical housing, and axes of the first and the second screen elements may be vertically arranged. Further, the first and the second screen elements may be coaxially arranged. The first screen can be positioned above the second screen element, and the suspension flow direction can be from an upper part of the housing to a lower part of the housing. Moreover, the first screen may be positioned axially outside of and above the second screen element, and the suspension flow direction can be from an upper part of the housing to a lower part of the housing.
According to another feature of the invention, the housing can include a vertical housing having an upper chamber and a lower chamber, such that the first screen element is positioned within the upper chamber and the second screen element is positioned within the lower chamber.
Further, the housing may be a horizontal housing, and axes of the first and the second screen elements can be horizontally arranged. The first and the second screen elements may be coaxially arranged. The first screen can be positioned upstream of the second screen element, relative to the suspension flow direction. The first screen may be positioned axially outside of the second screen element.
The housing can include a horizontal housing having an first chamber positioned upstream from a second chamber, relative to the suspension flow direction, such that the first screen element is positioned within the first chamber and the second screen element is positioned within the second chamber.
In accordance with still another feature according to the instant invention, the opening angle (xcex1) can be between about 60xc2x0 and 120xc2x0.
According to a further feature of the present invention, the second screen element can be fixed in the housing.
A centrally aligned light reject outlet may be coupled to the housing. The light reject outlet can be located in a region of the first screen element. The first screen element may be arranged in the housing to form an intake chamber outside of the first screen element, and the light reject outlet may be located in the intake chamber. Further, the light reject outlet can include a closable valve that automatically opens for a short time at intervals. A rotor can be arranged to drive the first screen element, such that no mounting structure is positioned between the first screen element and the light reject outlet.
The first screen element may include a double conical form in which a diameter of the double conical form increases in the suspension flow direction.
A diameter of the conical shape may increase in the suspension flow direction.
Moreover, a diameter of the conical shape of the first screen element can increase in a direction toward the second screen element.
Fixed screen scrapers can be located on a throughput side of the first screen element.
According to another feature of the present invention, fixed scrapers may be located on an inlet side of the first screen element.
In accordance with still another feature of the instant invention, an inlet side of the first screen element can have a profiled surface.
In accordance with a further feature of the invention, an inlet side of the first screen element can be equipped with bars.
The first screen element can include round holes having a diameter of at least about 2 mm. Preferably, the round holes can have a diameter of at least about 4 mm. Further, at least some of the round holes may have a diameter of at least about 4 mm.
The first screen element may include screen openings having different sizes in accordance with a radial position on the first screen element. The screen openings can increase in size as the radial position of the screen opening is farther out.
At least one flow guide element can be located in an intake chamber adjacent the first screen element. The at least one flow guide element can be arranged to influence peripheral movement of the suspension in the intake chamber. Further, at least one flow guide element can include arched surfaces arranged to divert a peripheral flow in the intake chamber radially toward a middle.
In accordance with the invention, the second screen element may include a cylindrical screen basket.
Further, the second screen element can include round screen openings having a diameter of no more than about 2 mm.
A rotor can be provided and scrapers can be coupled to the rotor. In this manner, the scrapers can be arranged for movement to keep the second screen element clear. The rotor may be coupled to rotatably drive the first screen element. Moreover, the rotor may move the scrapers at speed different than a rotational speed of the first screen element.
In accordance with a further feature, a first and a second rotor can be provided. The first rotor can be coupled to the first screen element to rotatably drive the first screen element, and the second rotor can be coupled to the scrapers to move the scrapers. The rotors may be coaxially arranged.
According to still another feature of the instant invention, the at least one intake can open tangentially into the housing.
In accordance with yet still another feature according to the present invention, a largest inside diameter of the first screen element can be larger than a largest inside diameter of the second screen element.
The present invention is directed to a process for removing contaminants from a contaminant-containing fibrous paper suspension. The process includes supplying the suspension containing contaminants into a pressurized screen, separating a coarse fraction of contaminants with a first rotating conical screen element, in which the conical screen has an opening angle of between about 10xc2x0 and 170xc2x0, separating a fine fraction of contaminants with a second screen element, and conveying the suspension without the coarse and fine contaminants out the pressurized screen.
In accordance with a feature of the invention, the coarse fraction separation can occur upstream of the fine fraction separation, relative to a suspension flow direction. Further, the coarse fraction separation may occur vertically above the fine fraction separation. Alternatively, the coarse fraction separation may occur horizontally adjacent the fine fraction separation.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.